Present telecommunication system technology includes a wide variety of wireless networking systems associated with both voice and data communications. An overview of several of these wireless networking systems is presented by Amitava Dutta-Roy, Communications Networks for Homes, IEEE Spectrum, pg. 26, December 1999. Therein, Dutta-Roy discusses several communication protocols in the 2.4 GHz band, including IEEE 802.11 direct-sequence spread spectrum (DSSS) and frequency-hopping (FHSS) protocols. A disadvantage of these protocols is the high overhead associated with their implementation. A less complex wireless protocol known as Shared Wireless Access Protocol (SWAP) also operates in the 2.4 GHz band. This protocol has been developed by the HomeRF Working Group and is supported by North American communications companies. The SWAP protocol uses frequency-hopping spread spectrum technology to produce a data rate of 1 Mb/sec. Another less complex protocol is named Bluetooth after a 10th century Scandinavian king who united several Danish kingdoms. This protocol also operates in the 2.4 GHz band and advantageously offers short-range wireless communication between Bluetooth devices without the need for a central network.
The Bluetooth protocol provides a 1 Mb/sec data rate with low energy consumption for battery powered devices operating in the 2.4 GHz ISM (industrial, scientific, medical) band. The current Bluetooth protocol provides a 10-meter range and a maximum asymmetric data transfer rate of 723 kb/sec. The protocol supports a maximum of three voice channels for synchronous, CVSD-encoded transmission at 64 kb/sec. The Bluetooth protocol treats all radios as peer units except for a unique 48-bit address. At the start of any connection, the initiating unit is a temporary master. This temporary assignment, however, may change after initial communications are established. Each master may have active connections of up to seven slaves. Such a connection between a master and one or more slaves forms a “piconet.” Link management allows communication between piconets, thereby forming “scattemets.” Typical Bluetooth master devices include cordless phone base stations, local area network (LAN) access points, laptop computers, or bridges to other networks. Bluetooth slave devices may include cordless handsets, cell phones, headsets, personal digital assistants, digital cameras, or computer peripherals such as printers, scanners, fax machines and other devices.
The Bluetooth protocol uses time-division duplex (TDD) to support bi-directional communication. Frequency hopping permits operation in noisy environments and permits multiple piconets to exist in close proximity. The frequency hopping scheme permits up to 1600 hops per second over 79 1-MHZ channels or the entire 2.4 GHz ISM spectrum. Various error correcting schemes permit data packet protection by ⅓ and ⅔ rate forward error correction. Further, Bluetooth uses retransmission of packets for guaranteed reliability. These schemes help correct data errors, but at the expense of throughput.
The Bluetooth protocol is specified in detail in Specification of the Bluetooth System, Version 1.0A, Jul. 26, 1999, which is incorporated herein by reference.
In wireless communication systems such as described above, the well-known disadvantageous phenomenon of fading is encountered. Conventional transmit diversity techniques can provide several dB's of gain to thereby at least partially overcome the fading problem. Some known transmit diversity schemes require an estimate of the channel at the transmitter, which estimate can be made from previous receptions at the same frequency. However, because the operating environment is not totally static, such estimates are sometimes not very accurate.
Another known technique for overcoming fading is antenna space time transmit diversity. An example of this technique is disclosed in U.S. Ser. No. 09/205,029 filed on Dec. 3, 1998 and incorporated herein by reference. The space time transmit diversity disclosed therein is bit level space time transmit diversity for use with linear modulation schemes such as QPSK modulation. However, bit level space time transmit diversity cannot be used in wireless communication systems that utilize non-linear modulation schemes, for example the GFSK modulation scheme utilized in Bluetooth systems.
It is therefore desirable to apply space time transmit diversity techniques in wireless communication systems that utilize nonlinear modulation.
The present invention applies space time transmit diversity to achieve diversity gains in wireless communication systems that utilize nonlinear modulation schemes. In particular, space time transmit diversity (STTD) is applied at the block level to an original block of bits advantageously to reduce the effects of fading in wireless communication systems that use nonlinear modulation schemes. At the receiving end, fading parameters are estimated and the properties of complex conjugates are utilized to produce a result that is representative of the original block of bits.